Step 1: Cook the spaghetti in boiling salted water along with the potato slices for 10 minutes.
Step 3: chop the green beans into 1 inch pieces and add to the saucepan with the pasta and potatoes.
Step 5: cook for 5 more minutes then drain well, but save some of the pasta water.
Step 7: return the ingredients to the saucepan, along with the pesto and 2 tablespoons of the starchy pasta water to make more of a sauce.
Step 9: top with parmesan if you can afford such a luxury!